Because I understand the mechanism of sea erosion as to take earth away from shorelines (and scatter it deep into the sea floor) and also to derive from climate crisis, I ask the following question:

Is sea erosion the opposite of sea level rising (or rather, an adjacent phenomenon)?

  • $\begingroup$ @JohnDoea heh, but seriously, the use of "opposite" doesn't make sense. If erosion is the opposite of sea level rising, that means they counteract each other, or cancel out to some extent. I can't see how they cancel out. Both of them decrease the amount of land. $\endgroup$ – user253751 Mar 3 at 17:26
  • $\begingroup$ Both decrease the amount of shore but one can assume that in some raise of sea level there would be less shore to erose. $\endgroup$ – user19055 Mar 3 at 17:37

A paper about this was published yesterday in Nature Climate Change: Sandy coastlines under threat of erosion (Vousdoukas et al. 2020).

While shoreline change can be the combined result of a wide range of potentially erosive or accretive factors, there is a clear cause and effect relationship between increasing sea levels and shoreline retreat, pointing to increased coastal erosion issues. Climate change will also affect waves and storm surges, which are important drivers of coastal morphology.

The study computes projections of shoreline retreat. They computed four projections: two for 2050, and two for 2100, depending on climate change scenarios (RCP 4.5 and RCP 8.5). Here are the results:

Assuming that there are no physical limits in potential coastal retreat, by mid-century we project a probable (5th–95th percentile) global average long-term shoreline change, ranging from –78.1 to –1.1 m and –98.1 to 0.3 m, under RCP 4.5 and RCP 8.5, respectively (negative values express erosion). By the end of the century the erosive trend becomes even more dominant and we project a probable range from –164.2 to –14.8 m and –240 to –35.3 m under RCP 4.5 and RCP 8.5, respectively.

And here is how it looks on a map (their figure 1):

Vousdoukas 2020 figure 1

The caption reads:

Projected long-term shoreline changes. a–d, Projected shoreline changes by the years 2050 (a,c) and 2100 (b,d) under RCP 4.5 (a,b) and RCP 8.5 (c,d). Values represent the median change and positive/negative values, respectively, express accretion/erosion in metres, relative to 2010. The global average median change is shown in the inset text for each case, along with the 5th–95th percentile range.

Note that this projected retreat is a combination of two factors: the ambient shoreline change (AC) driven by geological, anthropogenic and other physical factors, and the shoreline retreat due to sea level rise (R). But R is the dominant factor, with a worldwide contribution of 82 % to the total retreat (with regional variations, see their figure 2).

In summary, climate change leads to sea level rise, which in turns leads to coastline erosion. Sea erosion is not the opposite of sea level rising, it is a direct consequence of it.

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There are a few facts I would like to bring to your attention. Sometimes a rising shoreline is due not only to rising sea levels but also to the land sinking. Southern England is very gradually sinking due to a seesaw effect caused by the rise of Scotland after the ice sheets melted. There are other phenomena which sometimes cause the land to rise, usually phenomena of a volcanic nature. Land has been rising around Vesuvius, for example. Earthquakes can cause it to sink.

When land sinks or sea level rises, a new area of land is exposed to coastal erosion. In most places it would have to be a very large rise to allow the sea to go far inland. Coastal erosion is not always loss. While some of the rocks and sediments are dragged into deep water and lost, it is often the case that substantial quantities are moved further along the coast, where the current slows down and deposits it, building up new land. This happens in Britain and no doubt in other countries too.

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  • $\begingroup$ Thank you for this nice answer, I gladly up voted. $\endgroup$ – user19055 Mar 3 at 13:33
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    $\begingroup$ While this answer is very interesting, you've provided neither sources nor substantiated you personal expertise. We are all subject to misperception, and I readily believe everything you've said. :-) $\endgroup$ – jpaugh Mar 3 at 17:13

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